\subsection{Feedback and Feedforward}
Feedback and feedforward are the two building blocks upon which all effects are based. Feedback and feedforward both serve more or less the same purpose but does so in two different ways, meaning that depending on the effect you are trying to achieve one will be more favorable to use than the other.

\subsubsection{Feedforward}
Feedforward, also known as an \textit{Finite Impulse Response (FIR)}, works by sending the incoming audio through a delay and then multiplying it with the current signal. That is, if someone is playing a signal, the player will both output the current part of the signal to the speakers, and at the same time it will also output the current part of the signal to a delayer, which buffers, or saves, that part of the signal for a certain amount of time. These two parts will then be multiplied to form a new signal that is transmitted through the speakers. A diagram of how this works can be seen in figure \ref{fig:feedforward}.

\begin{figure}[htbp]
\centering
\includegraphics[width=0.7\textwidth]{images/TheoryDesign/feedforward.png}
\caption{Diagram of how feedforward works.}
\label{fig:feedforward}
\end{figure}

\subsubsection{Feedback}
Feedback, also known as \textit{Infinite Impulse Response (IIR)}, as the name implies, does more or less the opposite thing of feedforward. While feedforward sends the delayed signal forward to be mixed with the original signal, feedback sends it backwards. The reason this is such a major difference is that when the delayed signal in a feedforward is multiplied with the current signal, it is sent to the output. When the delayed signal in a feedback is multiplied with the current signal it happens behind the point where the feedback catches the signal to delay, or in other words, the multiplication happens before the feedback samples the signal. This means that the multiplied signal is send through the feedback constantly, until the feedback is turned off. If this is not controlled, it can result in very high pitches being sent out like one sometimes hear when placing a microphone too close to a speaker. A diagram of how this works can be seen in figure \ref{fig:feedback}

\begin{figure}[htbp]
\centering
\includegraphics[width=0.7\textwidth]{images/TheoryDesign/feedback.png}
\caption{Diagram of how feedback works.}
\label{fig:feedback}
\end{figure}

Feedback is often used in filters, because even though it requires the user to know a bit more about how it works and to be a bit more careful it also have the explained features which makes it more ideal. Using a feedforward filter with a big amount of terms (e.g. 99) can be used to design a filter with precise linear phase. This means that all frequencies are equally delayed. On the other hand, a feedback filter is harder to design and can give phase distortion \cite{understandDSP}.